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sample_exams_Exam_1_Key - ‘22 CHEM 241 SAMPLE EXAM#1 1(5...

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Unformatted text preview: ‘22,. CHEM 241 SAMPLE EXAM #1 1.(5 pts) In the recrystallization lab you cooled the solution from boiling to 0 °C. What would be the consequence of only cooling this solution to 35 0C instead of 0 °C? Air 35%, 4M solxmri bum/dot otlsmliu. WWWpouna ii’wm art 0°C, ~‘1LM Wot/dd 2. (6 pts) What would be the consequence of trying to carry out a recrystallization of a mixture that was 60% compound to be purified and 40% organic impurity? m (Xmomvx‘i‘ CE "Mpuwrb is ire; («wk/TV“; tampon/\va would C""“’V"IS7L’"”'ZJZ (M’H‘l “Ru 0mm) Compan 3. (6 pts) In the acid base extraction lab, why did you use 6 M NaOH instead of 1M NaOH to neutralized the acid extracts? “5‘er 6M MO“ Wang own halt/J QM 7: Small boium % 4M Mayor} In OVOU/x ’i‘b mot-Miliy _HIV_. Sblu’hbw .3 (1614 Make, (JAG quey fif‘HVvQVW ’i'o at V , _ . i LSsole V‘uw/ Cvapounce —Q}W‘~:l\ Q’cfa le‘i/xh data/$43- 4. (6 pts) In the acid/base extraction lab what was the structure of the compound that was isol—a when you neutralized the acidic extracts with 6 M NaOH? “H’I/ u 43f ‘& Questions 5, 6 and 7 refer to compounds A-H below. 0 O H C O \ \/\/\/OH 3 Wok A CH c .4 B 3 .’ bp 120 bp 101 D CI mp 76 mp 131 Br NHZ COzH O Q G mp145 H E F COZH bp 45 mp 125 mp 185 5. Equal amounts of A, C and H were mixed together and the mixture is distilled. a) (6 pts) What would be the order in which each compound would be distilled over (first, second and third)? H‘MQMC-HWA b) (8 pts) Circle the gas chromatography trace depicted below which would most liker represent the 1st mL fraction collected from a simple distillation of A,C and H. 5 c. (8 pts) Draw what the Temp vs Volume graph of this distillation would look like if all 3 compounds (A,C and H) were completely separated. Be sure to denote appropriate temperatures and volumes. Assume that the volume of the original mixture was 30 mL and that there are equal proportions of each compound in the mixture. 1/ (Om) 7.0»! 3’0sz 6. You have a 1:121 mixture of B, E and G and you will purify this mixture by acid/base extraction. You dissolve all 3 in diethyl ether. You then extract the ether layers 2 times with 1 M NaOH (you mix then separate from the ether layer). a) (6 pts) Depict the species (draw the chemical structure) that is dissolved in the 1 M NaOH solution. #0 '2 O l »C. 0’ \Da “0‘3 b)(6 pts) If you wanted to isolate (as a solid) the compound that is dissolved in the l M NaOH solution in 6 a, what would you do next? A0191 (3M HCl {"0 rePVfi+MWEQ COmPoz/uvi {Catch ta‘H/u. onSnrm/l oxiwl «col/m. 7. a.If you were to brominates compound F, what would be the product(s) of this reaction if it went through a bromonium ion intermediate? b. What would the products be if it was a carbocation intermediate? H H COL C07. 0“ 6V (01H “ a N ‘ I"! ) Br 9.’ b on.” COL” (01H CD‘LH . I B“ l 3» (131,14 wild 1,, + 8" + In B», ' 8r 3" Br ’1, 8 5/ All it tn [ill/4’ amom/Hlj 9.(6 pts) A faulty recrystallization procedure is given below in which there is one procedural error. Point out this error and explain what is wrong with it. Also make the appropriate correction to the procedure. Propanol, heated to 750 C, is added to an impure sample of toluic acid until all of the solid just dissolves. The solution is then slowly cooled to 0° C. The solvent is then removed by centrifugation. The boiling point of propanol is 970 C and the melting point of toluic acid is 1100 C. / PVOchnbi BOXlTWZ (970C) '~ "1H ewdl {‘0 deoe (MO Ob Tt x ‘ "to OilSSOlN falumcaud —; 7A1 Wain 5/0 Maudfla- 10. The graphs below show solubility behavior of m—toluic acid and benzophenone in methylene chloride, acetone and ethanol. Use this data to answer a and b. a) (8 pts) Would it be possible to recrystallize a mixture of 85% Toluic acid and 15% Benzophenone using methylene chloride as the solvent? x—Hi-yee—atiw'haf-peint-woitfid'flr , C as;' 6 vv' " ;- ..-, - , . . h . “fi'eensifiung ) ._ (bid. b) (6 pts) What would be the solvent of choice to recrystallize a mixture of 90% Benzophenone and 10% toluic acid? _ . €‘H4c‘ \n A l (methylene chloride methanol . T Graph for m—toluic acid solubilty (g/mL) /———-—‘ acetone / Temp ————> / A ethanol r ______/ methylene chloride Graph for benzophenone solubilty (g/mL) ___________..._—————--—“ acetone / Temp 11. Using the solubility data for the solubility of dibromobenzene in the solvent methanol is shown below. Using this data calculate a and b Temp Solubility (g/mL) 60 °C 0.5 g/ml 50 °C 0.4 g/mL 40 °C 0.3 g/mL 30 °C 0.2 g/mL 20 °C 0.1 g/mL 10 0C 0.04 g/ mL a. (6 pts) How much methanol would be required to dissolve 1.5 g of biphenyl. At 60 °C. @ 3W“ X (9—53 ._ l-S“ 011550le. 4,“. :3 b. (6 pts) How much biphenyl would remain in solution if it were cooled to 20 °C? ‘ 0.93 0 remain; V‘x Sblu’i‘wm‘ o ENLX G.i j Ml 12. (6 pts) What is the difference between precipitation and crystallization? Pat \Px‘i‘c’rww '13” («5‘1 Cymbal 4va Ma (1,“ «cm H flap [MPMV‘HZS CVfichllgalfli/k {5 Slaw ’ Seac‘i‘iw (.vdrh‘l QVMLAHA, he) impwr “(3) \ 13 Draw a flow chart to depict the separation of F, E and D. ...
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